How to know LINE (not polyline) direction?

[iPranavKulkarni]

I created rectangle shape by line and I want to know the direction (clockwise or anticlockwise).
Can someone pls help.

[_gile]

Hi,

Clockwise and counterclockwise does not make sense for a single line.

You should work with polyline or points (summits of the rectangle).

You can check if a polygon (points sequence) is clockwise or counterclockwise by computing its signed area. If the area is negative, the polygon is clockwise.

Here's an example which computes both the polygon centroid and signed area.

        public static Point2d GetPolygonCentroid(Point2dCollection polygon, out double area)
        {
            Point2d cen = new Point2d();
            double tmpArea;
            area = 0.0;
            int last = polygon.Count - 1;
            Point2d p0 = polygon[0];

            for (int i = 1; i < last; i++)
            {
                var p1 = polygon[i];
                var p2 = polygon[i + 1];
                tmpArea = GetTriangleSignedArea(p0, p1, p2);
                cen += (GetTriangleCentroid(p0, p1, p2) * tmpArea).GetAsVector();
                area += tmpArea;
            }
            return cen.DivideBy(area);
        }

        public static Point2d GetTriangleCentroid(Point2d pt0, Point2d pt1, Point2d pt2) =>
            (pt0 + pt1.GetAsVector() + pt2.GetAsVector()) / 3.0;

        public static double GetTriangleSignedArea(Point2d pt0, Point2d pt1, Point2d pt2) =>
            ((pt1.X - pt0.X) * (pt2.Y - pt0.Y) -
            (pt2.X - pt0.X) * (pt1.Y - pt0.Y)) / 2.0;

A testing command:

        [CommandMethod("CENTROID")]
        public static void Centroid()
        {
            var ed = Application.DocumentManager.MdiActiveDocument.Editor;

            var ppo = new PromptPointOptions("\nPick a point: ");
            ppo.AllowNone = true;
            var points = new Point2dCollection();
            while (true)
            {
                var ppr = ed.GetPoint(ppo);
                if (ppr.Status == PromptStatus.None) break;
                if (ppr.Status != PromptStatus.OK) return;
                points.Add(new Point2d(ppr.Value.X, ppr.Value.Y));
            }
            if (2 < points.Count)
            {
                var centroid = GetPolygonCentroid(points, out double area);
                ed.Command("_point", new Point3d(centroid.X, centroid.Y, 0.0));
                ed.WriteMessage($"\nArea = {Math.Abs(area)} ({(area < 0.0 ? "Clockwise" : "Counterclockwise")})");
            }
        }

[iPranavKulkarni]

@_gile Thanks for your response. 
Actually Maximum times I am using lines because that is the requirement.

I am placing some objects on lines/polylines. using below piece of code I am inserting object.

double angle = Vector3d.XAxis.GetAngleTo(li.StartPoint.GetVectorTo(li.EndPoint), Vector3d.ZAxis);
                double length = li.StartPoint.DistanceTo(li.EndPoint);
                pt = li.GetPointAtDist(length * 0.5);
                using (BlockReference br = new BlockReference(pt, ObjId))
                {
                    br.Rotation = angle;
                    BlockTableRecord blkTblRec = (BlockTableRecord)trans.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
                    ObjectId brId = blkTblRec.AppendEntity(br);
                    trans.AddNewlyCreatedDBObject(br, true);
                }

problem is objects position changing with direction of line.

1.Line drawn CW direction so object placed at left side of line

2.line drawn CCW direction and object place at right side of line.

I need parameter from which I can get direction of line.

[_gile]

As said upper the line 'direction' only make sense for clockwise or counterclockwise when it's compared to the other lines componing the polygon.

[kerry_w_brown]

@iPranavKulkarni ,

Hi,

1.Line drawn CW direction so object placed at left side of line

2.line drawn CCW direction and object place at right side of line.

I need parameter from which I can get direction of line.

You do have the direction of the line. !!

Seems to me you're complaining about the programming language not being able to guess what you want.
As Gile explained, the location and rotation of the block is being determined by what you tell it to do.
If you want it to be different you will need to program it to be different.
Perhaps you will need to incorporate a prompt asking for the user to accept ( or mirror ) the block properties.

Regards,